Subscriber (pay) TV systems often operate on the basis of entitlements stored in the form of data either in a decoder at a receiver, or in a detachable control access system such as a so-called "smart card". The subscriber/user gains access to a given program only if the description of the current broadcast program is consistent with the entitled fights owned by the user. The entitlements are updated "over-the-air", whereby data, often in encrypted form, are sent together with scrambled program information such as scrambled video. Data analysis by the access control system updates the current entitlements status of the user. However, if the user is not tuned to the channel carrying such "over-the-air" data while data dedicated to the user are being transmitted, such data are lost, and the program provider usually has no knowledge of the loss. The program provider therefore does not know the current entitlement status of the users.
Two currently used solutions to this addressing problem are as follows. The first solution involves sending the entitlement data more than once. This method is efficient and, from the standpoint of material cost, implies no price impairment. However, the bandwidth necessary to transmit the entitlement rights is drastically increased, or, for the same bandwidth, the time needed to update a complete population is significant. Furthermore, there is no way to know if the data were received. A second method uses a "back link". In this case the decoder may be equipped with a modem or with a modulator in a cable network environment. The decoder can "phone" the subscriber management center to confirm reception of the entitlement rights. However, this approach is expensive since the cost of the decoder is increased and the subscriber management center has to be equipped with an expensive automatic phone center.